How Breastfeeding Affects Your Hormones, Thyroid, & Nutrient Needs

Breastfeeding creates a whole new set of demands on your body, long after pregnancy is over. Behind the scenes, it creates a unique hormonal environment that can influence everything from ovulation and your menstrual cycle to thyroid function and nutrient needs. After the significant nutritional demands of pregnancy, breastfeeding continues to increase the resource requirements from your body.

Many of these changes are a normal and necessary part of supporting milk production and your growing baby. But they can also contribute to, or sometimes mask, issues like hormone imbalances, thyroid dysfunction, and nutrient depletion that may leave you feeling less than your best as you recover postpartum.

So, what actually happens to your hormones, thyroid, and nutrient levels while breastfeeding? Understanding these changes can help you make sense of how you’re feeling, interpret your health more accurately postpartum, and recognize when your body may be asking for additional support.

 

Breastfeeding Changes Your Hormonal Landscape

One of the biggest hormonal changes associated with breastfeeding involves prolactin, the hormone responsible for stimulating breast milk production.

Every time your baby nurses, signals from nipple stimulation travel to the brain and trigger the release of prolactin from the pituitary gland. Frequent nursing or pumping can therefore keep prolactin elevated throughout the breastfeeding period. Even intermittent breastfeeding produces acute surges in prolactin.

Prolactin doesn’t operate in isolation, and is part of a variety of hormone cascades. The hormonal signals involved in breastfeeding also suppress activity within the hypothalamic-pituitary-ovarian (HPO) axis, the communication system between your brain and ovaries, which regulates ovulation and reproductive hormone production.

High prolactin levels contribute to decreased gonadotropin-releasing hormone (GnRH) signaling from the hypothalamus in the brain. This reduces luteinizing hormone (LH) signaling from the pituitary, which can delay follicle development and ovulation.

What’s the downstream result of this altered hormone activity in the brain? Estrogen and progesterone can remain significantly lower while breastfeeding, particularly during periods of frequent or exclusive breastfeeding.

Low estrogen can contribute to symptoms such as vaginal dryness, changes in libido, and delayed menstrual cycles. Progesterone remains low when ovulation hasn’t resumed because progesterone is primarily produced by the corpus luteum following ovulation.

This is why many women don’t get their periods back for months after giving birth, and why even if your menstrual cycle returns, this doesn’t necessarily mean that ovulation and hormone production have immediately returned to their pre-pregnancy patterns.

 

What Happens to Your Thyroid While Breastfeeding?

Thyroid health becomes especially interesting postpartum because several changes are happening simultaneously.

During pregnancy, thyroid hormone production increases significantly to meet the demands of both mom and baby. After delivery, thyroid activity begins shifting back toward a non-pregnant state.

At the same time, the immune system undergoes another major transition. Pregnancy requires significant adaptations in immune activity to support the developing baby. After delivery, immune activity shifts again, which can increase susceptibility to autoimmune thyroid dysfunction. This is one reason postpartum thyroiditis is more likely to develop during the first year after pregnancy.

Postpartum thyroiditis may initially cause a temporary increase in thyroid activity and thyroid hormones, creating a hyperthyroid state. This is then followed by a drop in thyroid function and a shift to a hypothyroid state several months later. For some women, thyroid function eventually normalizes, while others develop persistent hypothyroidism postpartum.

Breastfeeding introduces an additional thyroid consideration: increased iodine requirements. Iodine is essential to produce thyroid hormones, and during breastfeeding, iodine is actively transported into breast milk to support your baby’s thyroid hormone production and neurological development. 

As a result, the recommended dietary allowance for iodine increases from 150 mcg per day in non-pregnant women to 290 mcg per day while breastfeeding. If dietary iodine intake isn’t sufficient to keep up with these increased demands, maternal iodine levels suffer, especially in individuals who entered pregnancy or postpartum with already low iodine stores. We often test iodine levels in our practice, and find that a vast majority of our patients have suboptimal or deficient iodine levels. 

This doesn’t mean more iodine is always better, however. Excessive iodine can also disrupt thyroid function, making appropriate intake and individualized assessment particularly important.

 

The Nutrient Demands of Breastfeeding

Growing a baby requires an enormous amount of nutritional resources, and those demands continue to increase after delivery, particularly if you are breastfeeding.

Breastfeeding continues transferring nutrients from mother to baby through breast milk. For those who entered pregnancy with nutrient deficiencies, became depleted during pregnancy, or have not had the time or support to adequately replenish postpartum, lactation can further increase nutritional demands and nutrient depletion.

Vitamin A is a great example. Vitamin A is a fat-soluble vitamin transferred into breast milk and plays an essential role in infant immune function, vision, cellular development, and growth. Maternal requirements therefore also increase substantially during lactation.

The recommended dietary allowance (RDA) for vitamin A nearly doubles when comparing levels for non-pregnant women compared to those who are breastfeeding. It’s not just critical for the baby’s development, but is also key for mom’s immune system as it undergoes significant changes postpartum.

Iodine and vitamin A aren’t the only nutrients worth considering. Breastfeeding also increases the need for several other vitamins and minerals involved in maternal recovery and infant development, including choline, vitamin B12, folate, zinc, and selenium.

Iron is a little different, but an important mineral to mention. The RDA actually decreases during lactation compared with pregnancy, largely because menstruation typically has not yet returned. 

However, iron needs can remain elevated for some women postpartum. Those who entered pregnancy with inadequate iron stores, developed anemia during pregnancy, or experienced significant blood loss during delivery may still be iron deficient postpartum. For this reason, assessing your iron status with the appropriate lab testing is especially important during pregnancy and postpartum.

 

Supporting Your Body Through Postpartum Recovery

Fatigue, hair loss, mood changes, brain fog, feeling cold, weight changes, and irregular cycles are often brushed off as “just normal postpartum symptoms.” But while some changes are expected after birth, common doesn’t mean normal, and these symptoms shouldn’t be dismissed.

Pregnancy, delivery, and breastfeeding place significant demands on the body. Nutrient stores may need to be replenished, thyroid function can shift, and reproductive hormones take time to find their new rhythm. 

If you’re navigating postpartum, whether breastfeeding or not, our 1:1 coaching program can help you better understand your symptoms and assess your health through comprehensive lab testing and a personalized, root-cause approach. Together, we can identify opportunities to optimize hormone and thyroid function, replenish nutrient stores, and provide your body with the support it needs to recover and thrive postpartum. Apply to work with us today!